Study On Chitosan Degradation By Application Of Pulsed Electric Field And Active Oxygen

Chitosan is the deacetylation product of chitin, and chitin is the second largest renewableresource just after cellulose on earth, also the largest number of nitrogen-containing naturalcompounds in addition to proteins. Oligochitosan is the hydrolysate of chitosan, and it isformed from2～10monosaccharides connected by glycosidic bond, which has highdissolubility, easily absorbed. Oligochitosan shows unique physiological activity andfunctional properties, when its molecular weight is less than3000Da. Meanwhile thepreparation of oligochitosan is always difficult for researches and manufactures.In this paper, the degradation of chitosan was investigated by the way of high voltage-pulsed electric field and the synergetic degradation with hydrogen peroxide or ozone. On thisbasis, the paper proposed the mechanism of chitosan degradation under the high-voltagepulsed electric field, and it can be referred to the researcher as a basis for following researchand industrial application. The main research contents and results are as follows:1. This is the first time to study the impact of high-voltage pulsed electric field on thechitosan degradation. Base on processing method of the pulse electric field, this paper hasstudied the effects of chitosan degradation by some factors, such as electric field strength,processing time, chitosan concentration, electrical conductivity, and so on. The results showedthat the average molecular weight of chitosan was decreased with the increase of electric fieldstrength and significant degradation effect was obtained under higher field strength. Forexample, the degradation rate reached54.2%when the field strength was33.3kV/cm; Thedegradation rate was slowing down gradually with time extended, and the degradation rates atthe first20minutes and the last70minutes were18.5%and8.5%, respectively. The increasedconcentration and conductivity of chitosan didn’t benefit the degradation of chitosan. Theanalysis of FTIR and X-ray diffraction showed that the side chain structure of chitosan wasnot changed before and after degradation, indicating that the basic chemical structure ofproducts was not changed.2. This paper has studied the impact of different processing time of hydrogen peroxide atthe certain concentration for the chitosan degradation. It was found that hydrogen peroxidehas significant effect on the chitosan degradation, and with increasing of processing time, themolecular weight of chitosan was decreased gradually, molecular weight distribution (Mw/Mn)was also showing a decreasing trend. However, the processing time for hydrogen peroxide onchitosan degradation was limited. Based on the above study, this paper studied the synergy degradation of chitosancombining with PEF and hydrogen peroxide. It was found that the synergic effect of PEF andhydrogen peroxide was obvious. After treated for60minutes, the degradation rates of PEFand hydrogen peroxide was25%and90.7%respectively, meanwhile the degradation rate ofcombination with PEF and hydrogen peroxide reached94.8%. When the electric field strengthwas increasing, the weight-averge molecular weight (Mw) of low molecular weight chitosanwas decreased, and the molecular weight distribution (Mw/Mn) was also decreased. Byanalyzing the FTIR of the original and degraded chitosan, we found that the basic chemicalstructure was not changed.3. This paper studied the impact of ozone on chitosan degradation, including the ozoneflux, processing time, concentration of chitosan. It was showed that the molecular weight ofchitosan decreasing with the increasing ozone flux until it was saturated. After that, thechitosan continued to degrade with the increasing processing time, but after30minutes,molecular weight of chitosan changed little.Therefore, the synergy degradation of chitosan with PEF and ozone was studied. It wasfound that the synergic effect of PEF and ozone was obvious for degradation of chitosan. Asthe processing time increasing, the weight of molecule has evidently decreased. For example,after being treated for40minutes, the molecular weight was below5000Da, which wasalmost the water-soluble product. After being treated for30minutes, the degradation rates ofPEF and ozone was20.5%and93.8%, respectively, while the degradation rate of thesynergetic effect of PEF and ozone reached to98.5%. And through analyses of GPC, FTIR andXRD, it was showed that the molecular weight was decreased and the crystalline region wasdestroyed, but the structure of acylamide remained the same.4. According to above research, a free radical theory is proposed to explain themechanism of chitosan degradation by PEF and its synergic effect. Pulsed electric filed isfound to be able to increase the number of hydroxyl free radical, oxygen free radical andhydrogen free radical in the solution, which can enhance the effect on β-1,4-glycosidic bond.The effects of PEF, hydrogen peroxide, ozone and their synergy can all increase the density offree radical, which improved the degradation rate of chitosan. Meanwhile, amino group wasprotonated in acetic acid solution, and under the condition of electric field, the chain ofchitosan was more stretched and much easier to be attacked by free radical.